1. Field of the Invention
The invention relates to induction machine and other rotating machinery thrust bearings. More particularly the present invention relates to methods and apparatus for selectively varying shaft preload bias force on motor lubricated mechanical thrust bearings that support the shafts, by selectively varying air gap between stationary and rotating magnet portions of permanent magnet bearings that provide shaft preload. Exemplary embodiments of the present invention are directed to selectively varying shaft preload bias force on upper thrust bearings in vertical shaft induction motors with variable air gap permanent magnets.
2. Description of the Prior Art
Known rotating machinery, including vertical shaft motors, utilizes lubricated mechanical bearings to support, a rotating shaft and rotor. The rotating shaft vertical axial and radial loads are often supported by one or more mechanical bearings mounted within a bearing bracket. In vertical shaft induction motors the bearing bracket is in turn located in the upper portion of the vertically oriented motor housing. In such motors a lower mechanical bearing at the bottom of the motor housing supports shaft radial loads. Exemplary lubricated mechanical bearing types utilized in rotating machinery, including vertical shaft induction motors, include rolling element anti-friction bearings (e.g., spherical-type) wherein the rolling elements are lubricated by a non-pressurized boundary film layer between the element and its associated bearing race, hydrodynamic journal or thrust bearings that generate self-supporting pressurized lubricant films and hydrostatic bearings that employ externally pressurized lubricant. Some axial thrust fluid bearings consume significant power as they support the rotor vertical/axial thrust loads. Those loads generate heat in the bearing lubricant and necessitate active cooling, which complicates equipment design and maintenance. Some applications are not suitable for bearing lubricant cooling equipment. Under such circumstances motor rotational speed and/or load have to be kept sufficiently low to avoid need for bearing cooling equipment, or makes none applicable at times. These operational challenges for vertical shaft induction motors are generally applicable to other types of rotating machinery thrust bearing applications, regardless of the rotating shaft orientation (i.e., vertical horizontal or any other angle axis of rotation).
A need exists for a method and apparatus that passively and selectively apply desired variable preload force on lubricated mechanical bearings in rotating machinery, including vertical shaft motors, without the need for bearing lubricant cooling equipment and energy consumption associated with the cooling equipment.
Another need exists for a method and apparatus that passively and selectively apply desired variable preload force on lubricated mechanical bearings in rotating machinery including vertical shaft induction motors, to decrease the proportion of the shaft load that must be supported by the mechanical bearings. In this manner the mechanical bearing service life may be prolonged, higher loads may be supported by the existing bearing size, and/or smaller bearings can be substituted for the existing bearing size during retrofitting service.
An additional need exists for a method and apparatus that passively and selectively apply desired variable preload force on rotating machinery lubricated mechanical bearings, including vertical shaft motor upper lubricated mechanical bearings, that can be added to existing machinery designs during initial manufacture or retrofitted to existing machines during a servicing/maintenance period.
Yet another need exists in the art for a method and apparatus that passively and selectively apply desired variable thrust preload force on rotating machinery lubricated mechanical bearings, including vertical shaft motor upper lubricated mechanical bearings, in response to changes in shaft load.